/Engine/Source/Runtime/Engine/Classes/Kismet/KismetStringLibrary.h
Finds the starting index of a substring in the a specified string
The index (starting from 0 if bSearchFromEnd is false) of the first occurence of the substring
static int32 FindSubstring ( const [FString](API\Runtime\Core\Containers\FString) & SearchIn, const [FString](API\Runtime\Core\Containers\FString) & Substring, bool bUseCase, bool bSearchFromEnd, int32 StartPosition )